Printed wiring board structures generally are constructed of a core upon which one or more layers carrying ceramic chips or leaded components are laminated. These circuit and chip-carrying layers usually are of metalized (copper clad) polymeric construction such as a polyamide, and can be stacked above and below the core material. In order to provide efficient operation within the wiring board structure, the core should perform favorably with respect to tensile modulus, thermal conductivity, and thermal expansion.
A common core construction now employed is a metal core fabricated as a layer of molybdenum having on each surface thereof a respective layer of copper. While this copper-molybdenum-copper core is satisfactory with respect to tensile modulus, thermal conductivity, and thermal expansion considerations, the weight of this prior-art core can be a significant disadvantage in weight-sensitive applications. Conversely, of course, any replacement core material whose attributes include light weight must still provide satisfactory strength, low coefficient of thermal expansion and heat-response characteristics in order to qualify for wiring board construction.
In view of the above described requirements, it is apparent that a need is present for a printed wiring board structure having a core fabricated to meet weight restraints while providing efficient wiring board performance. Accordingly, a primary object of the present invention is to provide an integrated printed wiring board structure with a core exhibiting high tensile modulus, high thermal conductivity, low coefficient of thermal expansion, and light weight while being compatible with both surface mount and plated through hole technology components and corresponding circuitry.
Another object of the present invention is to provide such a printed wiring board structure whose core construction includes an organic matrix having disposed therein pitch based graphite fibers.
These and other objects of the present invention will become apparent throughout the description thereof which now follows.